I was dumping yeast I had big volcanic eruption through my blow off, what happened?

From what he is describing it sounds like he had the Chronicle filled to the very tip top (despite him saying there was only 22L in the vessel), and then when he tried to dump the yeast it created some positive pressure by releasing most of the dissolved CO2 in the beer. Since most of the active yeast in lager strains is at the bottom of the vessel, he likely "roused" the cake and created a pretty large release of head pressure. On top of that since it was an Oktoberfest it probably had a good amount of Dextrine in the beer, contributing to the beer heading-up, and reacting negatively to a relatively small blow-off to exit.

I would advise he avoid a trub dump with lagers since he will in turn dump a large share of active yeast. Since lagers typically don't have a lot of hop related trub, there isn't a huge appreciable benefit to a trub dump, even a few days in. On top of that, lager strains are less active then ale strains, so he'll likely need all the yeast he can get. Especially with only a 1 liter starter; in my opinion he under-pitched by about 50-60%. 30 mins of aeration was a bit overkill too, the end result will probably be oxidized beer anyway since the lager strain he's using likely cant consume all of the O2 before the fermentation is done on a 1.058 wort.

Its not my intention to pick apart his brewing process, but I can almost guarantee the vessel was overfilled and the crack of the valve roused the yeast cake, at which point all bets were off.

On 11/9/15, 2:03 AM, Edward

>Hello,>>I recently had an unexpected reaction in my 7 gal chronical and was>wondering if you have any explanation as to what happened.>>I've just completed my fifth AG brew of an Oktoberfest lager and its been>happily bubbling away into the blowoff at 12C for two days. In the>morning I attempted to drop out any trub from the bottom valve, but as>soon as I opened the valve the slightest amount, it gave out a huge>bubbling sound inside and beer violently shot out the blowoff hose like a>tap and even around the lid which was clamped down. I lost 3l of beer in>a matter of seconds!>>Up to this point the beer was being very well behaved. OG 1.058, 22l in>26.5l conical, open into 19mm ID silicone blowoff. Wyeast 2308 Munich>Lager 1st gen made up with single step 1l starter with 100g DME, chilled>and wort decanted. Wort aeriated with stone and air pump for 30mins>prior to pitching both at 16C before slowly dropping temp to 12C,>bubbling away before 24hrs in.>>Seems to have erupted with enough pressure to bend the steel clamps, they>felt loose after and I had to reshape them with a pair of screwdrivers to>get the lid to seal properly again.>>This has made me a bit nervous of opening the valves during active>fermentation!>>>Regards>>Edward